Neutral safety switch trouble-shooting?

[sneakypete]

Hi folks,
My check engine light has been on since I bought my car last year with a P0705 code on it. Now that it is time to get it inspected, I am finally trying to deal with it. I tested the electrical continuity of the plug that attaches to the sensor on the headlight side of the tranny bell housing, and it's good. I also tested the clutch pedal switch on the fire wall, and that is good too. The switch on the opposite side of the pedal had intermittent continuity, so I replaced it. I drove a few miles after hooking the battery up again, and the CEL is illuminated again.
Any thoughts? This is kind of urgent: I don't have a license plate, and I only have 8 more days to pass inspection.

 

[pcb]

This is what the manual says to do.
It sounds pretty elaborate for a simple circuit. I would try checking for a bad connection or a short to ground at the #64 pin on the PCM. I don't know what that 'breakout box' is but I'm pretty sure you can just check the voltage right at the harness with it plugged in. I'm thinking there is bad wire somewhere between the PCM and the neutral switch,... either broken or shorted. If you find it's that wire I would just snip it at the PCM (with enough left to solder in a new piece) and run a new length of wire all the way to the neutral switch.

procedure
DTC P0705 Neutral switch circuit malfunction
STEP INSPECTION ACTION

1 VERIFY FREEZE FRAME DATA HAS BEEN RECORDED
• Has FREEZE FRAME DATA been recorded?
Yes Go to next step.
No Record FREEZE FRAME DATA on repair order, then go to next step.

2 VERIFY RELATED REPAIR INFORMATION AVAILABILITY
• Check for related Service Bulletins availability.
• Is any related repair information available?
Yes Perform repair or diagnosis according to available repair information.
• If vehicle is not repaired, go to next step.
No Go to next step.

3 INSPECT NEUTRAL SWITCH SIGNAL CIRCUIT FOR SHORT TO POWER
• Connect breakout box with PCM connector disconnected.
• Disconnect neutral switch connector.
• Turn ignition key to ON (engine OFF).
• Measure voltage between breakout box terminal 64 (harness-side) and body ground.
• Is voltage B+?
Yes Repair or replace harness for short to power, then go to
Step 9.
No Go to next step.

4 INSPECT NEUTRAL SWITCH CONNECTOR FOR POOR CONNECTION
• Turn ignition key to OFF.
• Disconnect neutral switch connector.
• Check for poor connection (damaged/pulled out terminals, corrosion, etc.).
• Is there malfunction?
Yes Repair or replace terminal, then go Step 9.
No Go to next step.
ON-BOARD DIAGNOSTIC [ENGINE CONTROL SYSTEM (FS)]

5 INSPECT NEUTRAL SWITCH SIGNAL CIRCUIT
FOR OPEN CIRCUIT
• Make sure to reconnect all disconnected connectors.
• Turn ignition key to ON (engine OFF).
• Measure voltage between neutral switch terminal A (harness-side) and body ground.
• Is voltage B+?
Yes Go to next step.
No Repair or replace neutral switch signal circuit for open, then go to Step 9.

6 INSPECT PCM CONNECTOR FOR POOR CONNECTION
• Turn ignition key to OFF.
• Disconnect PCM connector.
• Check for poor connection at terminal 64 (damaged/pulled-out terminals, corrosion,etc.).
• Is there malfunction?
Yes Repair terminal, then go to Step 9.
No Go to next step.

7 INSPECT NEUTRAL SWITCH CONNECTOR CIRCUIT FOR OPEN CIRCUIT
• Disconnect neutral switch connector.
• Turn ignition key to ON (engine OFF).
• Depress clutch pedal and measure voltage between neutral switch terminal A (harness side) and body ground.
• Is voltage below 1.0 V?
Yes Go to next step.
No Repair or replace harness for open, then go to Step 9.

8 INSPECT NEUTRAL SWITCH SIGNAL CIRCUIT FOR OPEN CIRCUIT
• Turn ignition key to OFF.
• Connect breakout box with PCM connector disconnected.
• Turn ignition key to ON (engine OFF).
• Depress clutch pedal and measure voltage between breakout box terminal 64 and body ground.
• Is voltage below 1.0 V?
Yes Go to next step.
No Repair or replace harness for open, then go to Step 9.

9 VERIFY TROUBLESHOOTING OF DTC P0705 COMPLETED
• Make sure to reconnect all disconnected connectors.
• Start engine.
• Clear DTC from PCM memory using WDS or equivalent.
• Drive vehicle above 30 km/h {19 mph} and stop vehicle.
• Depress and release clutch pedal more than 10 times during drive cycle.
• Is same DTC present?
Yes Replace PCM, then go to next step.
No Go to next step.

10 VERIFY AFTER REPAIR PROCEDURE
• Perform “After Repair Procedure”. (See 01–02B–9 AFTER REPAIR PROCEDURE [FS].)
• Is there any DTC present?
Yes Go to applicable DTC inspection.
(See 01–02B–15 DTC TABLE [FS].)
No Troubleshooting completed.

 

[sneakypete]

What is the PCM?

 

[pcb]

That's the main computer that runs just about everything. It's located near where the feet of the passenger would be under the carpet on the fire wall. That number pin is apparently pink with a green stripe. That connector on the computer had 104 pins and wires on it, There is four pink wires on that side of the harness but the one you want has a green stripe on it. It's the pink wire closest to the middle of the connector on the second row with another pink wire with a black stripe right below it on the bottom row of the connector. The service manual shows the pin location on page 01–02B–126. I don't know how to copy pictures or diagrams. All I can manage to copy from a PDF file is the text. There is more info and diagrams in the P5 wiring manual if you have it.
I would try disconnecting the big connector on the computer and test for continuity between that pink wire and ground then see what it does in and out of neutral,... Power and key off for sure. MAKE SURE that you disconnect the battery negative if you unplug the PCM,... they make that clear in the removal chapter.
By the way,... there is a separate code (mil #704) for the clutch switch so your problem is almost for sure in the neutral switch circuit.
There is a PCM removal and inspection chapter in the service manual page 01-40b-7. (although I can't find what PCM actually stands for I'm thinking something- control module).

PS. I found out what the breaker box is,.. it's just a box you plug in between the PCM and the connector plug that gives you easy access to every pin out for testing, so you don't have to put your test leads into the harness itself. It just makes things easier but isn't necessary.

 

[sneakypete]

Ohh Ok, the part also known as the ECU or ECM. I know hot to access that. I work all day, but I will have my electrically-inclined roommate check it out tomorrow.

 

[pcb]

I'm pretty sure it's just a bad wire. I hope it didn't short out then fry the circuit in the ECU,... then you'd have to replace the ECU.

 

[sneakypete]

I have no driveability issues whatsoever, which is why I never took care of this, so I am pretty sure it isn't the ECU (ECM, PCM, W/E), which is actually the part out of an MP3. But now my apathy is biting me in the ass.
From searching the forum and reading about other people with the same error code, I think you are right about it being a bad wire. I will show my resident electrician your advice and have him give it a go. Thanks for the input.

 

[sneakypete]

If there is a short in the wire when I test it at the ECU, where do I need to trace it to? In other words, how much wire am I replacing and where does it go?
Also, can anyone tell me where the actual neutral safety switch is? I looked at an exploded diagram of the tranny, and I just can't find it.

 

[pcb]

Test for 12 V right at the ecu then test for that same 12 V at the other end of the wire at the connector (in and out of neutral). If there is no 12 V at the ECU then disconnect the battery Neg. and then the big ECU connector and test the pink wire for continuity (ohms) to see if it's shorted to ground or broken.
I'm almost positive that the switch is on the bell housing at the front facing the bumper. It's near the oil filler hole but higher and more towards the middle of the car. You can see the two wires coming out of it but I don't think there is a pink one until the other side of the connector. Don't forget to test the switch itself, it just unscrews and there is no gear oil gushing out of the hole or anything.

I did it once on my tracker,... my brake light was blowing a fuse because it was shorted to ground somewhere between the brake switch and the brake lights. It's really hard to find where it happened so I just cut the wire at the switch and at the brake light and replaced the entire length.
If your wire is bad I would just cut it near the ECU, and solder (or maybe a butt clip thing) a length of wire and just feed it through any where any way till it gets to the neutral switch and solder (or clip) it to the last couple of inches of wire on the switch. You could try to follow the original wire to attach it up along it's length but it doesn't really matter.
There is a picture and testing procedure on page 01–40B–43 of the FSM. It looks like the full length of the wire up to the connector at the switch is pink with a green stripe. The other wire goes right to ground.

 

[pcb]

I think I managed to figure out how to post a picture,... I'll give it a go,...

View attachment 201122

View attachment 201123

Well I'm still figuring this out,... the pictures for you are #62 and #63,... I need to figure out photo bucket to get the pictures right in the thread,...

Anyway,... the switch itself is right beside the gear oil filler plug,... it has two green wires up until it goes into the connector under the rad hose (pic 62). I would just disconnect at the connector and test for continuity down through the green wires heading to the switch,... no need to unscrew it. Just test for ohms in and out of gear and make sure it switches (I don't know if the switch is open or closed when in gear, but it doesn't matter as long as it switches when shifting in and out of gear)

Then you can test for 12 V at the connector between the pink and other wire when the ignition is turned on. I'm thinking your pink wire is bad somewhere between the connector and the ECU. If that's the case just snip the pink wire two inches from the connector, splice in a new wire and feed it through the engine bay and fire wall then attach it about two inches from the other end of the pink wire at the ECU,... cut the wire at the ECU too.
It may still be the switch itself which is easy to test and replace if necessary.
Rock-auto doesn't seem to have a neutral switch for a standard transmission,.. just the one for the automatic. You may have to go to the dealer if you need one.

 

[P-Funk!]

Y'all are making this too hard IMHO...

1. Jumper the switch at the connector. Fix it?
2. Jumper the switch at the connector and check for continuity at the ECM connector (above).
3. (This me only - do not attempt this on your on car or it will explode and kill people ) Jumper the wires at the ECU and don't try to start the car when in gear (no dummy-lock out feature any more )
3a. Run two new wires (i would just use speaker wire) from the switch to the ECU (bypassing all the wire harness) and keep the dummy feature )

 

[pcb]

Yea,.. just simply replacing both wires as a pair makes sense to me but I don't think just jumpering at the connector will work. The ECU needs to see that the switch is actually switching from open to closed 10 times to prove that it is working.
Your number 2 makes sense too and sounds a lot easier and straight forward.

I'm pretty sure the ECU uses one of the clutch switches for the dummy lockout and not the neutral switch (I can start my car in or out of gear but the clutch has to be pushed). The neutral switch is used in other ways,... It tells the ECU that you aren't in gear so it switches the engine over to idle so your engine doesn't race or stall (It may also kick out the cruise control along with the brake and clutch switch,... I suppose you could pull it out of gear without using the clutch so the ECU can monitor for that)

 

[P-Funk!]

ah - ok.

I did not know that about the ECU checking switch function... GTK

 

[pcb]

ah - ok.

I did not know that about the ECU checking switch function... GTK

Yea,... that's what gives the CEL in the first place.

 

[sneakypete]

We can't find the path of the wires from the switch and to the PCM. We just want to replace them, but can't trace them. Do you guys know?

 

[pcb]

You don't need to trace them,... test the switch at the connector then splice the wires at the connector then feed that pair of wires to the ECU and splice back in.
You can start at either end,... cut the two wires at the ECU, splice in your twin lead speaker wire then just feed it through the fire wall then to the connector under the rad hose or all the way to the last couple of inches of the neutral switch wire and splice back in.

 

[pcb]

Just find your own path to and from the ECU,... it doesn't matter. Just splice in to the two wires at the ECU (cutting the old ones off) then feed the twin lead speaker wire (if that's what you're using) all the way to the connector or even right to the last couple of inches of the neutral switch itself and splice back in.

(OOops I double posted,... I thought I lost the first one)


Don't forget to test for continuity of the switch itself,... it should be open then closed in and out of gear.

 

[sneakypete]

We fixed it!
The first thing we tested was the continuity of the switch itself, of course. That was good. Then ensued hours of tracing wires from the connector to different junction blocks to the ECU, and none of the pin numbers or wire colors seemed to match the wiring diagram. We were going crazy. But finally, all we ended up needing to do was to delete the connector and splice in some short lengths of wire in its place. I fired up the car and followed the testing protocol for the neutral safety switch, going over 20 mph and shifting in and out of neutral 10+ times. I drove about 10 miles, shifting in and out of neutral like 100 times, and the CEL did not come back on. If it does, this thread will get longer. Hopefully not though...

 

[sneakypete]

Thanks for the help, folks! I love this community.

 

[sneakypete]

For what it's worth to anyone searching this thread for the solution to their p0705 code, the neutral safety switch is on the firewall side of the tranny, not the headlight side. The reverse light switch is on the headlight side. Access the neutral safety switch from underneath the car.